A distribution system is a network of water pipes, power and storage devices delivering finished water from a water plant to individual users (i.e., residential, commercials, governments, schools and industries). Typically, well or river water is pumped to a water plant for treatment and production. Finished water is then pumped to a water storage tower and flows into a network of pipes toward the end users. Total length for a typical distribution network can be in hundreds of thousand miles. Inside of the pipe flows the water under pressure that can change in geographic locations and vary between time of a day and seasons.
Contaminant detection in a distribution pipe network is the subject of this said invention. Contaminants can be introduced into a distribution system in intentional sabotage, terrorist attack, accident or in naturally occurring incidences such as negative pressure siphoning in broken pipes (AWWA (2004) Verification and control of pressure transients and intrusion in distribution systems. AWWA Research Foundation, CO.). In such occasions, contaminated water volume is small compared to water flows inside of the pipe. After entering the pipe, contaminants of a finite volume disperse and transport in the form of a contaminated water body or “slug”. At the same time they react with chemical disinfectants that are added to water in compliance of drinking water regulations. A consolidated review of distribution system, disinfectants, and contaminant transport is given in U.S. EPA (2006) Water distribution system analysis: Field studies, modeling and management, a reference guide for utilities. U.S. Environmental Protection Agency, Water Resources and Water Supply Division, Cincinnati, Ohio.
Contaminants in the pipe can cause changes in water quality parameters due to their reactions with the water or even by merely simple mixing. Types of measured parameters that can reflect water quality change include total chlorine, free chlorine, chloride, nitrogen, pH, oxidation-reduction potential (ORP), conductivity, turbidity, and dissolved oxygen (DO). Online water quality sensors are commonly used in measurements. Total organic carbon (TOC) analyzer has been used for detection, but not commonly because of its high capital and operational cost. Furthermore, more advanced compound-specific sensors are under development (U.S. EPA (2005) Technologies and techniques for early warning systems to monitor and evaluate drinking water quality: A state-of-the-art review. Final Draft, U.S. Environmental Protection Agency, Office of Water, Washington, D.C., 165p.). At its current form, the said invention relies on conventional water quality sensors.
Two approaches for contaminant detection in water pipes have been proposed. One school uses conventional water quality sensors. Available commercial products such as the Hach Inc. EventMonitor™ fall into this category. Their sophistication varies in contaminant detection, but most identify outliers and anomalies using control chart (e.g., average and standard deviation) or similar statistical techniques. Some products also use comparison of historical variations. Limited to conventional statistical techniques, these commercially available methods and products have high false detection rates some in excess of 30-50%. In collaboration with the U.S. EPA, the Department of Energy (DOE) Sandia National Laboratory (SNL) is incorporating higher levels of statistical methods in anomaly detection. Their methods of multi-variable classification can achieve better results (Klise, et al, (2006) Water quality change detection: multivariate classification and discrimination algorithms. In proc. SPIE 06 Defense & Security, Orlando, Fla.), potentially around 10-20%.
Another school of approach is to develop and employ compound specific advanced sensors and instruments. These technologies are based on more advanced detection mechanisms (U.S. EPA, 2005 supra), and capable of providing accurate detection of a target contaminant in drinking water. At this time, no products are available for a wide range of hazardous contaminants in commercial scales. Even when available they are likely to be expensive and require skillful operation and maintenance, a practicality limitation for wide applications.
There is a need to detect contaminants introduced to water pipes and also to measure sudden changes in water quality that can lead to non-compliances of drinking water regulations. One advantage afforded in the present invention is its low false identification rates. The target rate is below 5%. A particular advantage to the present invention is the use conventional water quality sensors rather than advanced sensors, offering advantages in cost and operational logistics